Proteins, including antibodies, have been used in drug therapy for the past twenty years. In order to achieve high therapeutic doses, antibodies are typically formulated at high concentrations (about 10 mg/ml to 100 mg/ml or greater) (Brekke, O. H. and Sandlie, I. (2003) Nat. Rev. Drug Discov. 2:52-62). Certain modes of protein administration typically require highly concentrated protein formulations. For example, subcutaneous administration of therapeutic antibodies are often formulated at concentrations greater than about 100 mg/ml. Some of these concentrated protein formulations develop an opalescent appearance at high concentrations, a property often referred to as opalescence (Schellekens, H. (2002) Nat. Rev. Drug Discov. 1:457-462).
An opalescent appearance in a concentrated protein solution may result from a variety of factors, including protein concentration, its effect in Rayleigh scatter, temperature, the nature of solute-solute interactions, among others. When a protein is susceptible to opalescence, the opalescent appearance usually increases as the protein concentration increases. The similarity of opalescent solutions to aggregated protein solutions has raised concerns with respect to its loss of protein activity and potential to cause immunogenicity in pharmaceutical formulations (Pinckard et al. (1967) Clin Exp. Immunol. 2:331-340; Robbins et al. (1987) Diabetes 36:838-845; Cleland et al. (1993) Crit. Rev. Therapeutic Drug Carrier Systems 10:307-377).
Thus, there is a need for developing formulations of highly concentrated therapeutic proteins, e.g., therapeutic antibodies, having reduced opalescence.